The objective of the research is to define possible controls for DNA biosynthesis during normal and abnormal growth. Most of the DNA polymerase Alpha activity from HeLa cells in S-phase has been isolated as a Mr 640,000 multiprotein form that is designated DNA polymerase Alpha2. The enzyme has been purified to electrophoretic homogeneity and resolved into its components that include; a Mr 180,000 polymerase Alpha subunit, a Mr 70,000 DNA primase, a Mr 69,000 3'---greater than 5' exonuclease, Mr 96,000 C1 and Mr 52,000 C2 primer-recognition proteins and Mr 92,000 Ap A binding protein. The interaction of DNA polymerase Alpha2 and other required proteins for the efficient and specific initiation of RNA primer synthesis will be defined. The conditions and protein requirements in addition to polymerase Alpha2 that are required for elongation of DNA chains with catalytic efficiency, processivity and fidelity will be ascertained. The enzymic and nonenzymic proteins in addition to DNA polymerase Alpha2 that are required for the replicationof SV40-DNA in vitro in the presence of T-antigen will be studied.